Objective test for running shoe cushioning deterioration

Question

Is there an objective test that I can use to determine the deterioration of my running shoes cushioning? I follow the rule of thumb and replace my shoes after about 500km. But some shoes feel like the cushioning deteriorate faster than others.

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Edit: In the answers, outsole and cushioning height is mentioned. While the outsole of my shoe is somehow noticable, how would I measure the cushioning height? From the side and the back, new and old shoe look the same. However measuring depth of the shoe inside, it looks like there is 3mm difference!

My new shoe (0km, bottom/left) vs. old shoe (500km+), outsole comparison and heel height comparison. The old shoe cushioning feels worse only after some distance (few km). I am a midfoot/heel striker and run on the road.

Note that the shoes are not perfectly size-aligned on the second image.

Answer 1

I usually have 8-900 km in pair of shoes...

After 100 km I measure the sole depth and when it is 10-20 % less - usually 3-4 mm after 8-900 km - I start looking for new shoes...

Very unscientific... but it works for me :-)

EDIT: By the way: Basically I use a normal ruler. I put in inside the shoe and measure the hight to the next shelf in my bookcase... Easy :-) I do this every 100 km or so.

Note that I usually apply a little bit of pressure on the ruler to make sure my custom made insole in properly positioned.

Also I don't measure anything the first 100 km to allow the shoe to "settle in" first..

Answer 2

As you note, the 500K notion is just a rule of thumb.

I am a pretty big guy (250+ pounds) and my shoes wear out much faster than 500K. I am lucky if I get 300K out of a pair. You can see the crushed and worn out sole (Of course some of that is my goofy running stride, leading to strange wear patterns).

So sole wear depth is another hint. As the sole wears out, you can assume the cushioning has gone with it as well.

Usually, if you compare a fresh pair, with a used pair, you can see how much the cushioning at the edges, has shrunken.

Answer 3

Scientific studies do not seem to support the seemingly commonsense idea that cushioning in your shoes protects you from injury: http://www.ncbi.nlm.nih.gov/pubmed/18801775 . When you run with less cushioning, your brain apparently subconsciously adjusts your stride to keep the forces the same. This suggests that you save your money and keep using a pair of shoes until it wears out.